MI6 spy Gareth Williams would have suffocated within three minutes after getting inside his sports holdall, an inquest has heard.
Poisoning and asphyxiation are the "foremost contenders" in solving the death riddle, pathologists said.
It also emerged scientists found traces of "at least" two unknown people in his upmarket London apartment despite evidence Mr Williams rarely invited people over.
Forensic expert Ros Hammond said there were hopes of a breakthrough "within a matter of weeks" from DNA tests on a green towel discovered in his kitchen.
"There's hope," she told Westminster Coroner's Court. "The tests are still in progress and there may be some promising results from those tests."
Ms Hammond said a third party would not necessarily have left any DNA on his red North Face bag and padlock.
But she added: "There's certainly evidence of at least two people other than Mr Williams on the samples tested."
The 31-year-old was probably suffocated or killed by a poison which disappeared in his system during decomposition, pathologist Benjamin Swift said.
Dr Swift said his post-mortem examination was hampered by levels of heat within the bag after radiators were mysteriously turned on in Mr Williams's top-floor flat in the middle of summer.
The inquest was adjourned until Tuesday. Coroner Fiona Wilcox is likely to deliver her verdict on Wednesday.